The present invention relates to a foam sheet obtained by widening a foam sheet foamed by heating and a method and an apparatus for widening a foam sheet.
Generally, in case where a foam sheet is heated and softened to form mold goods, the mold goods have been sometimes wrinkled in accordance with the slackening phenomenon (draw-down) of the foam sheet caused by the self-weight of the foam sheet, or the thickness of the foam sheet has not been uniform, so that the commercial value of the mold goods is deteriorated.
Thus, in order to obtain a foam sheet in which a draw-down phenomenon thereof at the time of thermally forming it, a technique has been conventionally known that a foam sheet obtained immediately after a foam sheet is foamed by heating in the manufacturing step thereof is widened.
As a method for widening a foam sheet obtained immediately after foaming a foam sheet which has not been yet widened, a sheet widening technique such as a technique using a belt-rotary type or disk rotary-type sheet widening apparatus has been known which is vacuum-attached to both the ends of a foam sheet to increase the width of the foam sheet (For example, refer to, Japanese Examined Patent Publication No. 48-9955).
As an alternative method for widening a foam sheet, a sheet widening method using a sheet widening apparatus has been known which is adapted to increase the width of the foam sheet while both the ends of the foam sheet are held by holding parts including a pair of rotary belt like supporters and a plurality of holding wheels for holding both the end parts of the foam sheet (For example, refer to Japanese Unexamined Patent Publication No. 2-72938).
However, the above mentioned conventional sheet widening techniques are methods for increasing the width of a foam sheet merely by a vacuum force or a holding power, and therefore, the foam sheet cannot be always held completely. Thus, a problem that the foam sheet is slipped or displaced upon widening or the foam sheet cannot be widened with a sufficient holding power is liable to arise.
Therefore, the foam sheet to be widened in accordance with these techniques can be widened only within the range of the holding power of the holding parts, so that a completely widened foam sheet cannot be obtained.
In the case of the sheet widening apparatus using the vacuum-attaching means, such a disadvantage arises that the apparatus is complicated or becomes large in size in order to obtain a satisfactory vacuum force.
Further, also in the case of the sheet widening apparatus using the holding parts for holding a foam sheet, a problem resides in that a mechanism becomes complicated due to the rotary belt like supporters or the plurality of holding wheels and the size of the apparatus is large. Particularly, in the case of the sheet widening technique using the holding parts, when the foam sheet is abruptly widened, the foam sheet cannot be held, and therefore, the foam sheet has been gradually widened along gently tapered loci over a long sheet receiving distance. In this case, however, only both the side parts of the foam sheet, namely, only the parts of the foam sheet held by the holding parts are liable to be widened and the foam sheet which is evenly widened all over the direction of width cannot be obtained. In addition, if the foam sheet is widened over the long sheet receiving distance, the foam sheet is cooled on the way of sheet receiving, so that it is necessary to prepare a special heat source for reheating the foam sheet and a temperature adjustment is difficult.